1. Field of the Invention
The present invention relates to an image pickup apparatus provided with two solid image pickup devices and particularly to an image pickup apparatus having two solid image pickup devices disposed at a distal end portion of an endoscope and an endoscope apparatus incorporated the same.
2. Description of the Related Art
An image pickup apparatus having an objective optical system and a solid image pickup device has been widely spread. For such an image pickup apparatus, high image quality of picked up observation images as well as size reduction depending on equipment to which the apparatus is applied are being desired.
As equipment to which the image pickup apparatus is applied is an endoscope apparatus, for example. The endoscope apparatus is provided with an insertion portion to be inserted into a body cavity, and the image pickup apparatus having an objective optical system and a solid image pickup device is disposed at a distal end portion of the insertion portion. In such an endoscope apparatus, the endoscope insertion portion is inserted into the body cavity, the image pickup apparatus in the distal end portion picks up an image of a digestive tract and the like in the body, and an operator can observe the picked up image on a monitor outside the body.
In the endoscope apparatus, a space in the distal end portion of the endoscope insertion portion is mainly occupied by the image pickup apparatus having the objective optical system and the solid image pickup device and an illumination optical system having a light guide and/or an optical device (or might further include channels depending on the type of the endoscope). Therefore, a diameter of the distal end portion of the endoscope insertion portion is substantially determined by sizes of these two members. In order to reduce the size of the image pickup apparatus, it is effective to reduce diameters of the distal end portion of the endoscope insertion portion and the insertion portion itself.
On the other hand, one of the methods to improve image quality of the image pickup apparatus is to increase the number of pixels of the solid image pickup device. However, if the number of pixels is increased, that inevitably increases the size of the solid image pickup device, and diameter reduction of the distal end portion of the endoscope insertion portion and the image quality improvement have a contradicting relation.
One of methods to solve the contradicting diameter reduction of the distal end portion and the image quality improvement is to employ a multi-plate structure in order to improve image quality by using a plurality of solid image pickup devices. The multi-plate structure used in the endoscope is suitable for an image pickup apparatus with a double-plate solid image pickup device structure (hereinafter referred to as a double-plate image pickup apparatus) using two pieces of solid image pickup devices considering the diameter reduction equivalent to a single-plate type. For example, a single-plate image pickup apparatus is provided with three types of color filters of red, green, blue or cyan, magenta, yellow in the solid image pickup device, and four pixels form a single color pixel.
On the other hand, the double-plate image pickup apparatus using two solid image pickup devices is provided with a prism applied with coating reflecting green and transmitting red and blue. In one of the two solid mage pickup devices, red and blue color filters are arranged in a stripe state in directions where red and blue are transmitted, while in the other solid image pickup device, monochromatic or green color filter is arranged in a direction where the above-mentioned green is reflected. By arranging the two solid image pickup devices as above, a pixel of each solid image pickup device forms one color pixel. Thereby, image quality can be improved by using two solid image pickup devices with fewer pixels.
Related arts of such double-plate image pickup apparatus include an image pickup apparatus for endoscope provided with two solid image pickup devices in a distal end portion of an endoscope as described in Japanese Patent Application Laid-Open Publication No. 2004-258497 and Japanese Patent Application Laid-Open Publication No. 2007-135951, for example.
In these related art double-plate image pickup apparatuses, incident light is divided into two optical paths and emitted by a prism unit in which two prisms are joined, and each of the emitted lights is received by the two solid image pickup devices so as to improve resolution of picked up observation images.
Here, by referring to FIG. 9, a configuration example of the related-art double-plate image pickup apparatus used for an endoscope will be described.
As shown in FIG. 9, a double-plate image pickup apparatus 101 disposed in a distal end portion of an endoscope is provided with a prism unit 102 and two solid image pickup devices 106, 107.
The prism unit 102 has a prism portion 103 provided with a first prism 104, a second prism 105. The first solid image pickup device 106 is provided on an outgoing face side of the first prism 104, while the second solid image pickup device 107 is provided on the outgoing face side of the second prism 105.
A first FPC (flexible printed circuit board) 108 on which an electronic component 110 is mounted is connected to the first solid image pickup device 106. A plurality of signal lines 116 constituting a first communication cable 118 are electrically connected to the first FPC 108.
On the other hand, a second FPC 109 on which an electronic component 111 is mounted is connected to the second solid image pickup device 107. A plurality of signal lines 117 constituting a second communication cable 119 are electrically connected to the second FPC 109.
A distal end portion on an incident light side of the prism unit 102 is fitted and fixed in a holding holder 112. A metal frame member 113 is provided on an outer circumferential face on a proximal end side of the holding holder 112 so as to include the first and second FPCs 108, 109. A heat shrinkable tube 114 is provided on the proximal end side of the holding holder 112. The heat shrinkable tube 114 covers up to an outer circumferential portion on the distal end side of the first and second communication cables 118, 119. A filler adhesive 115 as a filler for protecting the image pickup apparatus 101 is disposed in the heat shrinkable tube 114.
As mentioned above, since the double-plate image pickup apparatus 101 has the two solid image pickup devices 106, 107 and is configured so that the two communication cables 118, 119 are electrically connected to the two solid image pickup devices 106, 107 through the FPCs 108, 109 as shown in FIG. 9, the apparatus is particularly effective in assembling performance of the image pickup apparatus.